[marcosdumay]

An union type is the C attempt to implement something like sum types, that other languages extend a bit to literally implement sum types.

Those two words live on different contexts, as unions are about a memory usage pattern, and sum types are about conceptual software design, but they often go together on the same language feature.

[munificent]

> An union type is the C attempt to implement something like sum types

Sum types, unions (in the C sense), and union types are three distinct concepts.

Wikipedia's article confusingly merges the latter two concepts together but they're different thing. TypeScript[1] and Scala[2] have union types, but they have nothing like C's notion of "unsafely reuse the same bits in memory to be interpreted as different things".

[1]: https://www.typescriptlang.org/docs/handbook/2/everyday-type...

[2]: https://dotty.epfl.ch/docs/reference/new-types/union-types.h...